Apparatus for detecting combustible gases



May 5, 1942,

{APPARATUS FOR DETECTING COMBUSTIBLE GASES J. N. BURDICK 2,281,746

Filed March 18, 1938 F IG. 3.

INVEN OR JOHN N. URDICK ATTO R N EY Patented May 5, 1942 APPARATUS FOR DETECTING COMBUSTIBLE GASES John N. Burdick, Buffalo, N. Y., assignor to The Linde Air Products Company, a corporation of Ohio Application March 18,1938, Serial No. 126,719

4 Claims.

The invention relates to a method and apparatus for the continuous and automatic detection of predetermined concentrations of carbonaceous constituents in gases or mixtures thereof and is particularly adapted for detecting the presence of hydrocarbons in so-called industrial atmospheres.

For the sake of simplicity and clarity, the present invention will be described in connectionwith the determination of hydrocarbons in certain industrial atmospheres, for example, atmospheres which are present in or about operations involving the production of liquefied gases. However, it will be apparent as the description proceeds that the invention is also applicable to various other situations.

In the manufacture of liquefied oxygen, certain concentrations of combustible impurities such as hydrocarbons in the air supply, if not detected in time, may lead to serious explosions. Apparently, such explosions are caused by the reaction between oxygen and the hydrocarbons which have accumulated in some part of the system and then have been ignited, spontaneously or otherwise. Analytical methods for determining the presence of hydrocarbons in the air supply prior to its introduction intothe system have heretofore been in use but for certain reasons these have been unsatisfactory. In the most common of such methods the hydrocarbons are converted to carbon dioxide, the carbon dioxide then absorbed in an alkaline solution and the solution finally titrated to determine its carbon dioxide concentration. Such a method is particularly unsatisfactory in industrial operations because it measures the actual amount of carbon dioxide only over a lengthy period. Consequently, in the event of a sudden influx of hydrocarbons in the air supply no knowledge of such a dangerous condition would be available until, perhaps, damage had been done. Further, the method is limited to intermittent operation and requires the presence of an operator during each determination. Finally, the apparatus necessary to carry out the method is bulky and requires considerable care and attention.

'An object of this invention' is to provide a method, free from the above disadvantages, for

the continuous and automatic detection of predetermined concentrations of carbonaceous constituents in gases or mixtures thereof.

Another object of the invention is to provide a compact and efficient apparatus suitable for carrying out the method of the invention.

These and other objects are attained in the method of the present invention which comprises the steps of purifying a gas or gaseous mixture, containing one or more carbonaceous constituents, of its objectionable acidic components; oxidizing saidconstituents to carbon dioxide;

intimately mixing said carbon dioxide with a solution, the color of which, by virtue of the presence of a soluble dye (indicator), varies in a definite degree with the carbon dioxide concentration, and automatically detecting the color variations in said solution caused by an increase in carbon dioxide above a predetermined concentration. It has been found that the color variations in said solution may be continuously detected by means of a photo-electric device responsive to such variations and that such a do vice may be connected, with or without current amplifiers, to a suitable alarm signal so that any increase in carbon dioxide concentration above a predetermined value will automatically actuate the alarm signal.

The invention will be more fully described in connection with the attached drawing in which:

Fig. 1 is a diagrammatic side view of a preferred form of anapparatus embodying the invention with one wall of the enclosing cabinet removed to disclose the interior;

Fig. 2 is a fragmentary sectional diagrammatic view, taken at Z--2 of Fig. 1, showing in detail the construction of an absorber B; and

Fig. 3 is a wiring diagram indicating the electrical circuit of the apparatus shown in Figs. 1 and 2.

To explain the respective function of the separate parts of the preferred form of the detector apparatus shown in the attached drawing, the operation of such an apparatus for the detection of hydrocarbons in air will be described by way of example.

safety trap ll, containing mercury or other suitable liquid, which serves to protect the apparatus from the building up of an excessively high pressure, to and through a trap I2 where carbon dioxide and other acidic gases are removed. The trap I! may suitably contain a granular, highly absorbent material consisting of a mixture of sodium hydroxide and asbestos. After leaving the trap I2, the gas sample is passed through a second trap l3 containing a material capable of absorbing ammonia, such material preferably consisting of silica gel moistened with dilute sulphuric acid. From the second trap 13, the sample passes to and through a saturator A which saturates the gas with water vapor. The saturator A suitably consists of a helical tube ll,

constantly filled by water from a chamber above requirements.

sample is led through a metal conduit 52 to a combustiontube 48 in which any hydrocarbons present in the sample are burned to carbon dioxide. For this combustion tube 43 Iprefer to employ a high-chromium-alloy steel tube which contains oxidized copper wire as a catalyst. The

combustion tube is externally heated in a furnace l6 to"a temperature of about 850 C. Asindi cated in Fig. 3, the furnace I 6 may be electrically heated, the heating current being controlled for instance by a resistance 45" and indicated by a meter 36.

The gas sample, now consisting entirely of oxygen, nitrogen, and carbon dioxide, is passed from the combustion tube 48 through ametal conduit 53 and a glass tube 54 into an indicator-solution contained in an absorber B. The absorber B, details of which are shown in Fig. 2, is made of glass and comprises a reservoir 20, a'sight chamber I 26, provided with two flat, parallel, opposed walls and a helical tube |1-, all of. which parts are kept substantially full of indicator solution by connection through a tube 28 and a threeway cook 21 to a liquid levellingchamber I8. The

gas sample passes into the helical tube l1 through a nozzle 38 and bubbles up through the tube l1 and the reservoir out into the atmosphere. The motion of the gas passing through-the Inchcal tubeproduces a circulation of the indicator solution up through the helical tube IT to the reservoir 20 and down through the sight chamber 26 to the bottom'of the helical tube l1. Solution may be drained from the absorber B by opening bon dioxide depends upon a rapid and reversible color change of the solution as gas samples of different carbon dioxide content bubble through it. Consequently, as a result of testing numerous solutions, a water solution of sodium bicarbonate and xylenol blue (p-xylenol sulphone phthalein),

which is blue at a pH of 9.2 and above, and yellow at a pH of 8.0 or lower was found to fulfill the In the preparation of the indicator solution it is desirable to prepare the following two separate solutions which are intermixed to make a single solution.

1. Sodium bicarbonate aqueous solution, 0.0005 normal.

2. A saturated aqueous solution of xylenol blue containing approximately 0.67 milligram of xylenol blue per cubic centimeter of solution. The proportions of the two solutions to be intermixed may be determined by the usual methods of pre-. paring pH indicator solutions. Although I prefer to employ a xylenol blue indicator solution, other indicator solutions, some of which are characterized by a color change other than'from blue to yellow, may also be suitably employed. Further, I do not wish to be restricted to the specific proportions herein shown, as indicator solutions having their ingredients in-proportions other than these will function satisfactorily.

. When a predetermined dangerous concentration ofhydrocarbons exists in the sample being tested, the indicator solution in the absorber-B an equivalent relay. A thermostat and an changes from a blue to a yellow color as the carbon dioxide gas reacts with the solution. When the hydrocarbon content of the sample returns to its value for normal operation, the color of the indicator solution likewise returns to its original blue color. The change of color may be observed visual1y,'and is also .used to actuate an automatic alarm in the following fashion. A beam of light from a light source 25 is directed by a suitable lens "system through the flat, parallel, opposed glass walls of the sight chamber 26, and through the indicator solution contained therein, onto the light receiving element of a photo-electric cell 2 I. Variations in the light transmitting power of the solution are detected by 'the photo-electric cell and thereby translated into variations in an electrical current. The light source 25 may consist of a watt 120 volt projection lamp, and the lens system 23 may be any conventional system suitable for focusing the light image in the center of the sight chamber 26. As shown-in Fig. 3, the light source 25 is provided with electric current by a transformer 30, and a variable resistance I9 is provided to control the light intensity.

. The operation of the photo-electric cell 2| and apparatus ancillary thereto is indic'ated'in Fig. 3. The cell 2| is preferably of the voltaic type, and this is the type shown in Fig. 3, but other types may be used if suitable changes in the auxiliary apparatus are made; The voltaic type cell 2| generates its own current when exposed to light in the visible spectrum and is used to operate a relay 33 of the DArsonval galvanometer type or electrical resistance heater 3| controlled by the thermostat 35 maintain the photo-electric cell 2| at a temperature conducive to efficient operation, suitably a temperature between F. and F. A resistance. 39 is inserted in series with the cell 2| and the relay 33 to limit the flow of electric current.

The relay 33 is used to control a circuit including an alarm horn 22 or other warning signal. Such circuit suitably comprises a source of direct current, such as a transformer 46 and a rectifier 41, a power relay 40, the horn 22, and electric current leads 24 containing switches 31 and 43.

When the concentration of carbon dioxide in the gas sample reaches a dangerous concentration, the color of the indicator solution in the sight chamber 26 changes from blue to yellow.

This change in color correspondingly alters the character of the light beam passing through the sight chamber 2 from the light source 25 to the photo-electric cell 2|. The electric current generated by thecell 2| is altered joy such change a in light, and the alteration in current closes the relay 33, permitting direct current to how through, and to close, the powerrelay 40. The closing of, the power relay 40 causes the alarm horn 22 to sound.

A relay 4|, normally open, is used in series with the light source 25 so that, if the light source fails, the relay 4| will close and sound the horn 22. A warning lamp is used to indicate that the switch 43 is open and no current is being supplied to 'the alarm hom circuit. A lamp 34 is placed inside the cabinet 29 for convenience in visually inspecting the color of th indicator solution in the absorber B.

- The relays 33, 40, and 4|, the rectifier 41, and

the transformers 30 and 46, are for convenience housed together in a suitable power-unit cabi-' net P.

If desired, direct current may be used to actuate the alarm horn 22, the lamps, and the furnace, in which case resistances may be substituted for the transformers 30 and 45, and the rectifier" will not be needed.

While I have disclosed in detail a preferred embodiment of my invention, it is obvious that without departing from the invention, many ,other embodiments may be made to adapt the method and apparatus of the invention to numerous situations. I For example, hydrocarbons in any non-combustible gas such as argon may readily be detected if a suitable amount of oxygen is added to the sample. For the detection of carbonaceous constituents in combustible gases, means, other than a high temperature catalyst, may be used to promote the oxidation to carbon dioxide. For example, carbon monoxide may be oxidized by the use of iodine pent oxide. By employing a suitable catalyst and temperature, certain combustible gases may be detected in the presence of other combustible gases when the latter gases are not affected under the conditions of oxidation. Also, the method and apparatus may readily 'be adapted to detect the presence of carbon dioxide in atmospheric gases, hydrogen, or hydrocarbon-gases, merely by omitting the combustion step.

I claim:

1. An apparatus for automatically detecting,

in the air supply for processes involving high compression of such air, the presence of oxidizable carbon dioxide-forming compounds in a concentration in excess of a predetermined safe limit, which comprises, in combination, means for continuously withdrawing a sample stream of such air; means for continuously treating said sample stream to oxidize to carbon dioxide, all oxidizable carbon dioxide-forming compounds present therein; a reversible absorbent for carbon dioxide which is capable of yielding up carbon dioxide to, or of absorbing carbon dioxide from, said sample stream in response to changes in concentration of carbon dioxide in said treated sample stream, and thus in accordance with corresponding changes in concentration of said compounds in said air supply, said absorbent also being capable of transmitting energy in vary-' ing degree depending on its carbon dioxide content and undergoing relatively abruptly a substantial change in energy transmitting proper ties in the region of carbon dioxide content thereof corresponding to said predetermined limit of concentration of oxidizable carbon dioxide-forming compounds in said air supply;

.means for continuously bringing said treated sample stream into intimate contact with said absorbent; means for transmitting through said absorbent; means, responsive to variations in energy transmitted through said absorbent, for continuously receiving at least a part of such transmitted energy; means, actuatable by said energy-responsive energy and signalling means, for indicating whenever said. absorbent,

abruptly undergoes substantial change in energy transmitting properties in said region.

2. An apparatus for automatically detecting,

.in the air supplyior procesess involving high" compression of such air, the presence at hydrocarbon in a concentration in excess of a predetermined safe limit, which comprises, in combination, means for continuously withdrawing a sample stream or such air; means ior continuousiy treating said sample stream to oxidizejo carin said region.

bon dioxide all hydrocarbon present therein; a reversible liquid absorbent for carbon dioxide which is capable of yielding up carbon dioxide to, or of absorbing carbon dioxide from, said sample stream in response to changes in concentration of carbon dioxide in said treated sample stream, and thus in accordance with corresponding changes in the hydrocarbon concentration in said air supply, said absorbent also being capable of transmitting light in varying degree depending on its carbon dioxide content and undergoing relatively abruptly a substantial change in light transmitting properties in the region of carbon dioxide content thereof corresponding to said predetermined limit of concentration of hydrocarbon in said air supply; means for continuously bringing said treated sample stream into intimate contact with said absorbent, means for transmitting light through said absorbent; means responsive to variations in light transmitted through said absorbent for continuously receiving at least a part of such.

transmitted light; and signalling means including a photoelectric cell for indicating whenever.

compression of such air, the presence of hydro-' carbon in a concentration in excess or a predetermined safe limit, which comprises, in combination, an inlet tube constructed and arranged for continuously withdrawing a sample stream of such air; a heated combustion tube containing a combustion catalyst for continuously treating said sample stream to oxidize to carbon dioxide all hydrocarbon present therein; an absorber vessel containing a water solution of sodium bicarbonate acting as a reversible liquid absorbent for carbon dioxide which is capable of yielding up carbon dioxide to, or of absorbing carbon dioxide from, said sample stream in response to changes in concentration of carbon dioxide in said treated sample stream, and thus in accordance with corresponding changes in the hydrocarbon concentration in said air supply, said absorbent also containing xylenol blue which makes said absorbent capable of transmitting light in varying degree depending on its carbon dioxide content and undergoing relatively abruptly a substantial change in. light transmitting properties in the region of carbon dioxide content thereof corresponding to said predetermined limit of concentration of hydrocarbon in said air supply; means for continuously bringing said treated sample stream into inti-" mate contact with said absorbent, means fortrolled by said photoelectric cell 1201- indicating 1 whenever said absorbent abruptly undergoes substantial change in light transmitting properties JOHN N. BURDICK. 

